Solving the crystal maze: The secrets of structure

CRYSTALS are objects of true and profound mystery. That’s not because they channel occult energies, or hold misty hints of the future in their limpid depths. Their puzzle is much less esoteric&colon; why are they as they are?

It is an incredibly basic question, yet physicists still struggle with it. Can we say why a given group of atoms prefers one particular arrangement over another? Can we predict how a crystal will be structured, and so deduce what properties it will have?

By and large, the answer is an embarrassing no. Or at least it used to be, if Chris Pickard of University College London is right. He has developed a surprisingly simple way of predicting crystal structures. His technique, along with another that has just emerged, might finally show us the way through the crystal maze.

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There is more at stake here than the prettiness of some multifaceted amethyst. Crystals occur within most materials around us, be they metals, rocks or our own bones. Crystal structures determine crystal properties&colon; the arrangement of atoms in a material makes it hard or soft, conducting or insulating. But theory alone has been unable to work out what those structures should be. “We have to rely on experiment,” says Pickard. “That always bugged me.”

With good reason. Sometimes X-rays and other probes just don’t reveal how a crystal is built, and materials in extreme situations such as other planetary cores are simply beyond the reach of experiment. Besides, if you could cook up crystals in a theoretical …